Fabrication of CZTS solar cells by sputtering method An experimental technique to measure the resistance change of ITO thin film during cyclic bending Reliability study of wafer level chip scale package using board level drop test

This thesis effort comprises three separate research topics. Topic one is a discussion on the fabrication of a certain variety of thin film solar cell by sputtering method. The absorber layer in these cells is CZTS (Copper Zinc Tin Sulfide) which is a p-type semiconductor. The advantage of CZTS based solar cells is that the materials used in its fabrication are inexpensive and non-toxic. Two methods namely co-sputtering and single target sputtering were employed to deposit CZTS. After completely fabricating the solar cell, the efficiency obtained from co-sputtering was found to be higher than from single target sputtering. Optimization studies can be used to improve solar cell performance from both methods.;The second topic in this thesis demonstrates a technique used to study the reliability of thin film ITO (Indium Tin Oxide) on PEN (Polyethylene Napthalate). ITO is a transparent conducting oxide and is used as an electrode in CIGS solar cells (Copper Indium Gallium Selenide). ITO on PEN has applications in the flexible solar cells, the reliability of which is essential to the overall functioning of the cell. Accelerated testing can be used to gauge the reliability of such a system. Instron tensile tester is used to perform bend testing on samples obtained from the CAMM center at Binghamton University (sheet resistance of 30-40 O/square). Tests like continuous bend test, cyclic bend test and dwell test were performed. Critical bending radius was found to be between 4.5 and 5mm. Variables like dwell time and crosshead speed are also considered. It was found that dwell time and crosshead speed did not affect resistance change.;The final topic discussed in this thesis is about the reliability study of wafer level chip scale package (WLCSP) using board level drop test. Test vehicles with two different thicknesses of under bump metallizations (in the ratio 1:3) were studied. Time zero characterization includes solder bump shear before and after reflow, optical microscopy and mechanical cross sectioning. Methods to characterize failure modes after board level drop test include X-Ray and optical microscopy, mechanical cross sectioning, Energy Dispersive X-Ray spectroscopy (EDS) and statistical analysis. Test vehicles were mounted on a standard JEDEC board (in a 5x3 array) and drop tested for a certain number of drops and failure modes were observed. Intermetallic compound failure and bulk solder failure were seen to occur. Results and Weibull analysis indicate that UBM type 2, with thicker under bump metallization is more reliable than UBM type 1.